There is a clear need for ongoing clinical research on bipolar disorder to identify more effective treatments. However, the primary affective symptoms, and deficits in insight and cognitive functioning that are often associated with this condition, may adversely affect the capacity of some patients to consent to participate in such research. With the exception of our preliminary data from a small circumscribed sample of middle-aged and older bipolar patients, there have been no published studies of capacity to consent to research among bipolar patients. The goals of the proposed longitudinal study are to identify the factors associated with the level and stability of capacity to consent to research among a clinically and demographically heterogeneous sample of 172 people with bipolar I or II disorder, as well as among 118 healthy comparison subjects (HCs). We will also evaluate the degree to which understanding of disclosed information can be improved through an interactive disclosure process. Using standard measures, decisional capacity, severity of psychopathology, insight deficits, and neuropsychological functioning will be systematically evaluated at baseline, 6-, 12-, and 26- week visits. We hypothesize that bipolar patients will show significant deficits in decisional capacity relative to HCs, but there will be considerable within-group heterogeneity; between person differences in decisional capacity will be more strongly related to level of cognitive deficits than to severity of psychopathology or insight deficits. However, within-person variability over time will be a function of changes in psychopathology and insight. We also hypothesize that the number of prior affective episodes will be related to worse decisional capacity, but that this relationship will be mediated by the deleterious effects of multiple affective episodes on cognitive functioning and that levels of understanding among all participants will improve through an iterative disclosure process. This study will have high public health and bioethical significance, as there remains a clear need for clinical research in bipolar disorder, but there is a lack of empirical data to guide policy and researchers regarding the ethical enrollment of such participants in terms of ensuring valid initial and continuing informed consent.